© 1981 by London Mathematical Society
Hilbert Functions and Pseudo-Rational Local Rings of Dimension Two
Department of Mathematics, University of Exeter North Park Road, Exeter EX4 4QE
Let Q be an analytically unramified Cohen-Macaulay local ring of dimension 2, with maximal ideal m and infinite residue field k. If a is an m-primary ideal of Q, a* will denote its integral closure,
(a) = l(Q/a*), e(a) will denote its multiplicity,
(a) = 2.
(a)e(a) and
(a) = lim
(an)/n. This paper uses explicit formulae for
(ar),
(arbs) related to earlier results of Narita to prove that
(ab) =
(a) +
(b), and that the identity
(ab) =
(a) +
(b) holding for all m-primary ideals a, b characterises the pseudo-rational local rings of J. Lipman among normal Q. This is used to prove a number of results concerning the normal genus of an ideal and pseudo-rational local rings. In the last section, an expression for
(a) is obtained in the case where Q is regular which is related to the theory of infinitely near points of D. G. Northcott.